Seems like this could be an interesting build! Definitely interested in how the GPU will look in the build. As for your search, I remember seeing some temperature controlled fans when I was looking online for a case fan.. It's not one box controlling multiple fans, but they could do the same thing?

Otherwise I'm still in the research phase, I made contact to my laser cutting, drop the price. I turned to 3D printing, and where happiness.
So I decided to challenge me on this mod, DO NOT DO THAT ASSEMBLY: 3D full study, 95% of parts made in 3D printing and final assembly.
The only changes to be cut and on the housing.

I fell on an article presenting a MOD inspired from Mac Pro 2013 using the "Lunar" dustbin for case, but with a very small configuration.
Some research later, I discovered an improved version , powerful configuration, compatible Hackintosh.This version with a few followers, so I followed all these worklogs.
I decide to make my version, by taking only best installations.